docs: def to_hmtk(self, use_centroid=True):
          '''
          Convert the content of the GCMT catalogue to a HMTK
          catalogue.
          '''
          self._preallocate_data_dict()
          for iloc, gcmt in enumerate(self.catalogue.gcmts):
              self.catalogue.data['eventID'][iloc] = iloc
  
              if use_centroid:
                  self.catalogue.data['year'][iloc] = \
                      gcmt.centroid.date.year
                  self.catalogue.data['month'][iloc] = \
                      gcmt.centroid.date.month
                  self.catalogue.data['day'][iloc] = \
                      gcmt.centroid.date.day
                  self.catalogue.data['hour'][iloc] = \
                      gcmt.centroid.time.hour
                  self.catalogue.data['minute'][iloc] = \
                      gcmt.centroid.time.minute
                  self.catalogue.data['second'][iloc] = \
                      gcmt.centroid.time.second
                  self.catalogue.data['longitude'][iloc] = \
                      gcmt.centroid.longitude
                  self.catalogue.data['latitude'][iloc] = \
                      gcmt.centroid.latitude
                  self.catalogue.data['depth'][iloc] = \
                      gcmt.centroid.depth
              else:
                  self.catalogue.data['year'][iloc] = \
                      gcmt.hypocentre.date.year
                  self.catalogue.data['month'][iloc] = \
                      gcmt.hypocentre.date.month
                  self.catalogue.data['day'][iloc] = \
                      gcmt.hypocentre.date.day
                  self.catalogue.data['hour'][iloc] = \
                      gcmt.hypocentre.time.hour
                  self.catalogue.data['minute'][iloc] = \
                      gcmt.hypocentre.time.minute
                  self.catalogue.data['second'][iloc] = \
                      gcmt.hypocentre.time.second
                  self.catalogue.data['longitude'][iloc] = \
                      gcmt.hypocentre.longitude
                  self.catalogue.data['latitude'][iloc] = \
                      gcmt.hypocentre.latitude
                  self.catalogue.data['depth'][iloc] = \
                      gcmt.hypocentre.depth
              # Moment, magnitude and relative errors
              self.catalogue.data['moment'][iloc] = gcmt.moment
              self.catalogue.data['magnitude'][iloc] = gcmt.magnitude
              self.catalogue.data['f_clvd'][iloc] = gcmt.f_clvd
              self.catalogue.data['e_rel'][iloc] = gcmt.e_rel
              self.catalogue.data['centroidID'][iloc] = gcmt.identifier
              # Nodal planes
              self.catalogue.data['strike1'][iloc] = \
                  gcmt.nodal_planes.nodal_plane_1['strike']
              self.catalogue.data['dip1'][iloc] = \
                  gcmt.nodal_planes.nodal_plane_1['dip']
              self.catalogue.data['rake1'][iloc] = \
                  gcmt.nodal_planes.nodal_plane_1['rake']
              self.catalogue.data['strike2'][iloc] = \
                  gcmt.nodal_planes.nodal_plane_2['strike']
              self.catalogue.data['dip2'][iloc] = \
                  gcmt.nodal_planes.nodal_plane_2['dip']
              self.catalogue.data['rake2'][iloc] = \
                  gcmt.nodal_planes.nodal_plane_2['rake']
              # Principal axes
              self.catalogue.data['eigenvalue_b'][iloc] = \
                  gcmt.principal_axes.b_axis['eigenvalue']
              self.catalogue.data['azimuth_b'][iloc] = \
                  gcmt.principal_axes.b_axis['azimuth']
              self.catalogue.data['plunge_b'][iloc] = \
                  gcmt.principal_axes.b_axis['plunge']
              self.catalogue.data['eigenvalue_p'][iloc] = \
                  gcmt.principal_axes.p_axis['eigenvalue']
              self.catalogue.data['azimuth_p'][iloc] = \
                  gcmt.principal_axes.p_axis['azimuth']
              self.catalogue.data['plunge_p'][iloc] = \
                  gcmt.principal_axes.p_axis['plunge']
              self.catalogue.data['eigenvalue_t'][iloc] = \
                  gcmt.principal_axes.t_axis['eigenvalue']
              self.catalogue.data['azimuth_t'][iloc] = \
                  gcmt.principal_axes.t_axis['azimuth']
              self.catalogue.data['plunge_t'][iloc] = \
                  gcmt.principal_axes.t_axis['plunge']
          return self.catalogue